Jaw-muscle electromyography during chewing in free-ranging mantled howling monkeys at La Pacifica, Costa Rica: A pilot study

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Studies of primate masticatory form, function and evolution typically segregate into one of two lines of research. The first involves lab-based studies on captive primates, using techniques such as electromyography (EMG), to quantify the dynamics of rhythmic mastication. The second line of research involves field studies aimed at capturing the diversity of primate feeding behaviors and diets. Combined, these research programs provide overwhelming and complementary evidence that diet and feeding have led to adaptive modifications of masticatory apparatus form throughout primate evolution. Despite their mutual insight into primate masticatory evolution, these research programs have never been fully integrated. Moreover, because jaw-muscle function is directly influenced by the mechanical properties of foods, laboratory studies suffer from the necessary assumption that they reliably replicate what animals experience in the wild. In order to integrate these two lines of research, the PIs will develop and test a novel system to record jaw-muscle activity in free-ranging mantled howler monkeys (Alouatta palliata) at La Pacifica, Costa Rica. The EMG data collected from these monkeys while they eat their natural diets will be correlated with the mechanical properties of these foods to determine how jaw-muscle function varies with food mechanical properties. Howler monkeys at La Pacifica make an ideal study sample because their feeding ecology has been well-documented in this natural habitat. Additionally, because their diet ranges from leaves to fruits, EMG data can be recorded during the mastication of foods with a range of structural and mechanical properties.The scientific merit of this project lies in its integrative approach to studying the evolutionary significance of musculoskeletal design in the primate masticatory apparatus. This project will be the first of its kind to combine lab-based techniques for recording jaw-muscle function with field research on primate feeding ecology. Data collected in this project will link between masticatory function, diet and natural feeding behaviors. By combining these various data, we can develop ecologically and functionally robust hypotheses of primate adaptations of the masticatory apparatus. Furthermore, these data will address whether existing lab-derived EMG data are a reasonable proxy of the natural environment that various primates might encounter. The broader impacts of this project are that it will provide educational opportunities to Costa Rican students and contribute to the conservation of A. palliata. Students will get hands-on training in field techniques, electromyography, and mechanical properties data collection and analysis. This integrative approach will provide them with a broad evolutionary framework for future work on primate ecology, functional morphology and conservation. This research will also benefit conservation management decisions regarding the long-term sustainability of these endangered primates in different microhabitats in Central and South America. Finally, this project is led by a minority female researcher, thereby contributing to minority representation in the sciences.